Ultra-Wideband, Multi-epoch Radio Study of the First Discovered `Main sequence Radio Pulse emitter' CU Vir

Abstract

Presence of large-scale surface magnetic field in early-type stars leads to several unique electromagnetic phenomena producing radiation over X-ray to radio bands. Among them, the rarest type of emission is electron cyclotron maser emission (ECME) observed as periodic, circularly polarized radio pulses. The phenomenon was first discovered in the hot magnetic star CU Vir. Past observations of this star led to the consensus that the star produces only right circularly polarized ECME, suggesting that only one magnetic hemisphere takes part in the phenomenon. Here we present the first ultra-wideband (0.4$-$4 GHz) study of this star using the upgraded Giant Metrewave Radio telescope and the Karl G. Jansky Very Large Array, which led to the surprising discovery of ECME of both circular polarizations up to around 1.5 GHz. The GHz observations also allowed us to infer that the upper ECME cut-off frequency is at $\gtrsim 5\mathrm{GHz}$. The sub-GHz observation led to the unexpected observation of more than two pairs of ECME pulses per rotation cycle. In addition, we report the discovery of a `giant pulse', and transient enhancements, which are potentially the first observational evidence of `centrifugal breakout' of plasma from the innermost part of the stellar magnetosphere. The stark contrast between the star's behavior at GHz and sub-GHz frequencies could either be due to propagation effects, a manifestation of varying magnetic field topology as a function of height, or a signature of an additional `ECME engine'.

Accepted for publication in ApJ

References in corpus (13)

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• Magnetic field topology of the unique chemically peculiar star CU Virginis
• A Panchromatic View of Brown Dwarf Aurorae
• Stellar magnetosphere reconstruction from radio data. Multi-frequency VLA observations and 3D-simulations of CU Virginis
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• Magnetic field topology and chemical abundance distributions of the young, rapidly rotating chemically peculiar star HR5624
• Discovery of electron cyclotron MASER emission from the magnetic Bp star HD 133880 with the Giant Metrewave Radio Telescope
• Detection of coherent emission from the Bp star HD 142990 at uGMRT frequencies
• HST/STIS analysis of the first main sequence pulsar CU Vir
• The Polarization Convention of the uGMRT in Band 4
• Spots and flares in hot main sequence stars

Cited by in corpus (3)

• A scaling relationship for non-thermal radio emission from ordered magnetospheres: from the top of the Main Sequence to planets
• Radio masers on WX UMa: hints of a Neptune-sized planet, or magnetospheric reconnection?
• Discovery of eight 'Main-sequence Radio Pulse emitters' using the GMRT: clues to the onset of coherent radio emission in hot magnetic stars